Last season, slug control in potatoes got complicated. We find out how control strategies can keep legal within a complex set of regulations. The 2009 potato season was a year of new molluscicide approvals together with a host of new restrictions. Some metaldehyde products regained approval after the active’s sudden revocation for use in potatoes late in 2008 due to EU Maximum Residue Levels. But with the return of metaldehyde came new label regulations on the number of applications allowed per season and more stringent harvest interval requirements. However, growers had more choice following the launch of a new 3% ferric phosphate pellet with great environmental credentials. Slug control programmes are now all about the maximum total dose of the active ingredients and matching applications to the variety, says Dougie Bain, Masstock potato specialist. “In a variety like Maris Piper – very attractive to slugs – if you’re not careful it’s extremely easy to exceed the maximum total dose of any one product – with many growers treating potatoes as many as five or six times. Growers must be especially vigilant since the guidelines from the Metaldehyde Stewardship Group (MSG) are based on a maximum total dose per calendar year rather than per crop, as on the product label,” explains Mr Bain. The implication of making mistakes with slug pellet applications is huge. Not sticking to the letter of the law can mean losing 3% of single farm payment – a risk not worth taking, he stresses. “Using different products of the same active but at different strengths is a dangerous game to play. You can’t rely on one active ingredient throughout the life of the crop anymore.” So what are the key points about the different active ingredients in the armoury? “Sluxx, 3% ferric phosphate, has an obvious environmental fit and was well received as an additional slug control option by packers because it fitted supermarket protocols so well,” says Mr Bain. Trying a new product on a high value crop may seem a leap of faith but it’s a product that cannot be ignored, he believes. “I used Sluxx as the first two applications in programmes and it has more flexibility than other actives as you can apply a greater maximum total dose – up to 28kg per ha.” Pellets tend not to stick around long enough to reach the point of breakdown because slugs seem to find them very attractive and eat them, observes Mr Bain and any pellets that are left uneaten by slugs eventually break down into iron and phosphate, available to the growing crop. With metaldehyde products, growers need to be very aware of the changes to label recommendations. The MSG last year produced guidelines to the effect that a hectare of land should receive no more than 700g of metaldehyde per calendar year, with no individual treatment exceeding 250g per hectare. “Different maximum numbers of applications are allowed for different products, depending on their strength. Growers must be careful to get the maximum dose right where they’ve used different metaldehyde products within the same year,” comments Mr Bain. Five metre no spread zones were introduced alongside any watercourses as a measure to reduce the risk of inadvertent pellet application. With headlands still vulnerable to slug damage, Sluxx provides a useful alternative in these situations as the only product without an advisory application restriction. “I tend to follow Sluxx application in early and mid-season with metaldehyde,” says Mr Bain. Metaldehyde has long been the farmers’ favourite, representing good efficacy and value. Using actives with completely different modes of action is good practice for an anti-resistance strategy, he adds. “On high risk varieties I finish the programme with one or two late applications of methiocarb when the haulm has gone and potatoes are still vulnerable to damage,” says Mr Bain, adding that harvest interval is another important legal requirement not to forget. For methiocarb the harvest interval is 18 days, metaldehyde products are again variable depending on the product and ferric phosphate, uniquely, has no harvest interval requirement. |